Abstract
Abstract. Abundance-based model evaluations with observations provide critical tests for the simulated mean state in models of intercontinental pollution transport, and under certain conditions may also offer constraints on model responses to emission changes. We compile multiyear measurements of peroxy acetyl nitrate (PAN) available from five mountaintop sites and apply them in a proof-of-concept approach that exploits an ensemble of global chemical transport models (HTAP1) to identify an observational “emergent constraint”. In April, when the signal from anthropogenic emissions on PAN is strongest, simulated PAN at northern midlatitude mountaintops correlates strongly with PAN source–receptor relationships (the response to 20 % reductions in precursor emissions within northern midlatitude continents; hereafter, SRRs). This finding implies that PAN measurements can provide constraints on PAN SRRs by limiting the SRR range to that spanned by the subset of models simulating PAN within the observed range. In some cases, regional anthropogenic volatile organic compound (AVOC) emissions, tracers of transport from different source regions, and SRRs for ozone also correlate with PAN SRRs. Given the large observed interannual variability in the limited available datasets, establishing strong constraints will require matching meteorology in the models to the PAN measurements. Application of this evaluation approach to the chemistry–climate models used to project changes in atmospheric composition will require routine, long-term mountaintop PAN measurements to discern both the climatological SRR signal and its interannual variability.
Highlights
Peroxy acetyl nitrate (PAN) is produced alongside ozone (O3) from photochemical reactions involving precursor emissions of nitrogen oxides (NOx) and non-methane volatile organic compounds (VOCs)
We examine the correlation across models between simulated PAN source–receptor relationships (SRRs) and regional anthropogenic emissions of VOCs (AVOCs; Fig. 5) or NOx (ANOx)
That the inter-model range in regional AVOC emissions explains as much as 64 % of the variation in PAN attributed to EU emissions, and at least 25 % of the variance in PAN attributed to the NA region (Fig. 5)
Summary
Peroxy acetyl nitrate (PAN) is produced alongside ozone (O3) from photochemical reactions involving precursor emissions of nitrogen oxides (NOx) and non-methane volatile organic compounds (VOCs). When a PAN-containing free-tropospheric air mass subsides, PAN thermally decomposes to release NOx and can facilitate O3 formation far downwind (Wild et al, 1996; Schultz et al, 1999; Jaeglé et al, 2003; Kotchenruther et al, 2001a; Hudman et al, 2004) Both PAN and O3 distributions over any northern midlatitude region reflect the combined influence of production from sources within the region and transport from outside that region. We borrow from the emergent constraint approach in climate science to show that correlations between simulated total PAN and SRRs for PAN are sufficiently strong to permit PAN measurements at mountaintop sites (one in each of the three major northern midlatitude source regions) to narrow the wide inter-model spread in estimates of PAN origin We assess the relationship between PAN and O3 SRRs (Sect. 6) and conclude with a summary and recommendations for future work based on our proofof-concept analysis (Sect. 7)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call